The present invention relates to an apparatus for regulating pressure in the hydraulic brake system for a vehicle via a brake master cylinder, and, more particularly, to an apparatus for regulating pressure in a hydraulic brake system, the apparatus causing the brake lining and brake shoe to approach each other, such that initial brake response time is reduced, braking efficiency is improved, the slip rate between the vehicle tires and the road is minimized, stopping distance is shortened, and the fluid in the brake master cylinder flows into the apparatus such that the pressure of the brake master cylinder is prevented from rapidly rising during emergency or other urgent application of the brakes.
As described in FIG. 1, in a typical vehicle hydraulic brake system, when the driver applies the brake pedal 1, hydraulic pressure rises in the master cylinder 3, which is typically a tandem master cylinder, and pressure is thereby transmitted to the wheel cylinder 7 through hydraulic line P. The brake shoe 9 is moveable so as to frictionally contact the brake drum 13 via pressure transmitted to the wheel cylinder 7, producing a braking force.
The master cylinder 3 comprises a piston 4, a piston cup 5, a check valve V and a return spring S. A reservoir tank 10 is typically located in close proximity to and communicates with the master cylinder 3, so as to provide a supply of brake fluid. In front of the piston 4 (to the left as viewed in FIG. 1) is located a rubber piston cup 5 to maintain the hydraulic pressure. In the rear (to the right as viewed in FIG. 1) of the piston 4 is located a piston packing 6 to prevent the leakage of brake fluid. If the pressure in the master cylinder 3 is sufficient to activate a check valve V, the check valve V opens and transmits pressure from the master cylinder to the wheel cylinder 7.
If driver releases the brake pedal 1, the piston 4 returns by virtue of return spring S. Upon such return, if the fluid pressure in the master cylinder 3 is sufficiently reduced, this pressure causes the check valve V to close, preventing return of brake fluid to the master cylinder 3. At the front of the piston cup 5 (to the left as viewed in FIG. 1), the pressure drops temporarily during return, and fluid flows into the master cylinder 3 via hole H, which is formed in the piston 4 and about the circumference of the piston cup 5, as described further with respect to FIG. 2. The availability of this flow ensures that the return of the piston 4 is not prevented or impaired due to low pressure in the master cylinder 3.
As the piston 4 returns, brake fluid is able to return to the reservoir tank 10 through the relief port 11 and the inlet port 12. The check valve V remains closed until the pressure in the master cylinder 3 reaches the set-pressure.
Improving the handling of an automobile requires both good acceleration and good deceleration, in turn necessitating a hydraulic brake system having superior characteristics. Such superior characteristics are especially important with respect to safety.
The brake system for a typical vehicle provides a great deal of stopping force, which is utilized to stop the revolution of the vehicle""s tires. However, this force can completely stop the vehicle""s tire rotation without stopping the vehicle, resulting to slippage of the tires on the road (wheel lock). Such slippage occurs when the slippage force on the tires is less than the braking force. This slippage force is calculated by multiplying the frictional coefficient between the tire and the road by the weight applied to the road via the tire.
Namely, frictional coefficient xcexc, is extremely low on slippery road surfaces, as occur with the presence of ice or snow, while xcexc is much higher on, for example, dry concrete roads. In general, varying by motor vehicle model and road surface, the slip rate has a maximum, from which it quickly drops off.
The formula for the slip rate is expressible as follows:                     Y        -        W            S        xc3x97    100    =  v
where:
Vxe2x88x92W=the velocity of wheel;
S=the rate of slip; and
V=the velocity of vehicle.
In other words, when the driver applies the brake, it is advisable to maintain the wheels in a state such that the braking force is maximized and just less than the force that causes wheel lock. Safety is reduced and the rate of vehicle deceleration is reduced, resulting in longer stopping distances, when wheel revolution stops and wheel lock occurs.
To help achieve this condition in existing vehicles, hydraulic pressure in the brake system is typically reduced for the rear wheels relative to the front wheels, which prevents handling instability that would otherwise be caused by premature locking of the rear wheels. In existing vehicles, appropriate hydraulic pressure to maintain this condition is achieved through use of the following valves, which are installed on certain portions of tandem brake master cylinders to improve the braking efficiency:
Check valvexe2x80x94this valve improves braking efficiency by preventing return of pressure to the tandem brake master cylinder below a certain predetermined pressure, leaving any remaining pressure in the brake hydraulic lines. As a result, air osmosis is prevented and initial response time is shortened.
P valve (proportioning valve)xe2x80x94this valve is used to control the increase of hydraulic pressure and the triggering pressure point for activation of the brakes. This valve reduces the hydraulic pressure increase rate for the rear wheels as the brake force transmitted from the piston increases.
G valvexe2x80x94this valve controls the pressure of hydraulic fluid transmitted to the rear wheels. The G valve, which uses a ball valve that moves in accordance with a decrease in velocity of the vehicle, causing transfer of pressure among an outlet portion and an inlet portion, resulting in variation in the effective piston area applying the braking pressure.
Load sensing proportioning valvexe2x80x94this valve is used to control the hydraulic pressure to the rear wheels, with the opening position of the valve simultaneously varying in relation to the car weight.
Metering valvexe2x80x94this valve is used to decrease the abrupt hydraulic pressure of the front disk brake in low hydraulic pressure situations by decreasing the hydraulic pressure transmitted to the front wheels until the hydraulic pressure transmitted to the rear wheels becomes higher than the tension of return spring of the rear brake shoe. With this feature, brake pad life is prolonged.
In addition, an anti-lock brake device is used to prevent wheel lock from occurring when, for example, a car is braked on a road with low friction. The anti-lock brake device decreases the stopping distance and helps with control of the car by maintaining the vehicle""s direction and enabling steering control by keeping the wheels at the ideal slip rate.
However, in the prior art, the method for controlling hydraulic pressure to obtain the proper braking force, except with regard to the anti-lock device, depends on the driver recognizing the need to provide the correct brake pedal effort and to know to apply the brakes in sufficient time. In an emergency, if a driver applies the brakes strongly (to increase the brake force), wheel lock can occur based on the abrupt pedal stroke and resultant increase in hydraulic brake pressure. The prior art addresses this problem with the use of valves that provide measured decrease of braking pressure and thereby enhance braking safety. However, even with these systems, if the hydraulic pressure increases abruptly in the tandem brake master cylinder, which is the starting point for building hydraulic pressure, wheel lockxe2x80x94the so-called xe2x80x9cskid statexe2x80x9dxe2x80x94can occur. In this event, stopping distance increases and braking safety decreases abruptly.
An object of the present invention is to provide an apparatus for regulating pressure in the hydraulic brake system that causes the brake lining and brake shoe to approach each other in such a manner that when a driver applies the brakes, the initial response time is shortened, braking efficiency is improved, the slip rate between the tire and the road is kept in the ideal state, stopping distance is shortened, and fluid in the tandem brake master cylinder flows into the inventive apparatus so as to prevent the pressure of the tandem brake master cylinder from rising too rapidly, even in the event of a driver urgently applying the brake pedal.
An embodiment of the present invention includes an apparatus characterized as follows: a head of a piston is inserted into an upper cylinder of a housing so as to slide within the cylinder and forming a pressure chamber between the upper surface of the housing and the head of the piston; a sealing member is placed in a groove formed on the circumference of the piston near the head, the sealing member preventing leakage of hydraulic fluid past the head of the piston; a fixing member is threadably secured about the lower part of the housing; the lower end of a rod for coupling to the piston is inserted in a projecting extension having a concave opening that is formed on the fixing member; a spring is placed between a shoulder on the piston and the fixing member in order to support the piston such that the spring is compressibly loaded to provide a constant opposing pressure between the piston and the fixing member; a pressure controller pad located between the spring and the upper surface of the fixing member; an inlet hole in the upper cylinder through which brake fluid is able to flow into the pressure chamber; and an air discharge valve in the upper chamber for bleeding air from the pressure chamber.
In an embodiment of the present invention, the lower end of the rod coupled to the piston is located at a distance from the bottom of the projecting concave extension of the fixing member such that the piston is capable of moving a fixed distance, the fixed distance being the distance between the bottom of the projecting concave and the lower end of the rod, the movement being opposite the spring pressure, and the movement occurring when the pressure in the pressure chamber is higher than the pressure loading of the spring.
In an embodiment of the present invention, movement of the piston is limited by a shoulder within the housing.
An embodiment of the present invention includes a pressure controller pad that controls any unbalance of the spring at its contact point with the fixing member and at the same time reduces the elastic resistance of the spring with respect to the housing and the fixing member.
In an embodiment of the present invention, as the rod moves relative to the projecting extension concave section, openings form and are closed in the wall of the projecting extension, through which air is able to pass.
In one embodiment, in which the apparatus of the present invention is directly connected to the brake master cylinder, an inlet hole is formed in the horizontal surface of the upper cylinder and an air discharge valve is secured on the side surface of the upper cylinder.
In one embodiment, in which the apparatus of the present invention is directly connected to the brake master cylinder, the inlet hole is directly attached to the tandem master cylinder. In another embodiment, in which the apparatus of the present invention is indirectly connected to the brake master cylinder, the pressure regulating device is connected to the master cylinder by a connecter and pipes.
In another embodiment, in which the apparatus of the present invention is indirectly connected to the brake master cylinder, two housing portions are formed into a single connected body.
In one embodiment, the apparatus of the present invention is located downstream of hydraulic fluid flow of top dead center of the tandem brake master cylinder in the advancing direction of the primary and the secondary ring figured cups.
An embodiment of the present invention includes bleeding air from the system, which is accomplished by raising the pressure of the tandem brake master cylinder, discharging pressure via the check valve, and compensating for pressure difference, such that a narrow gap is maintained between the brake lining and the drum.